Goals
Understand what find and findIndex do
Write your own version of find and findIndex
Find
Iterates through an array
Runs a callback on each value in the array
If the callback returns true at any point, return the value in the array that we’re iterating over
Otherwise, return undefined
An Example
let arr = [1,2,3];
arr.find(function(value, index, array){
return value === 2;
});
// 2
let arr = [1,2,3];
arr.find(function(value, index, array){
return value < 1;
});
// undefined
JavaScript
How Does It Work?
Iterates through an array
Runs a callback on each value in the array
If the callback returns true at any point, return the value we’re iterating over
Otherwise, return undefined
function find(array, callback){
for(let i = 0; i < array.length; i++){
if(callback(array[i], i, array) === true){
return array[i]
}
}
}
JavaScript
Using Find In A Function
function findOddNumber(arr){
return arr.find(function(value){
return value % 2 !== 0
});
}
findOddNumber([2,3,4,5]) // 3
findOddNumber([4,6,8,10]) // undefined
JavaScript
function ensureNoSubArrays(arr){
return arr.find(Array.isArray) === undefined
}
ensureNoSubArrays([1, 2, [3,4]]); // false
ensureNoSubArrays([1,2,3,4]); // true
JavaScript
When You Would Use Find
You need to determine if a value in an array exists and you have to determine this by using a callback
A simple alternative to using filter and accessing the first element of the filtered array
findIndex
Iterates through an array
Runs a callback on each value in the array
If the callback returns true for any single value, return the index at which that value is found
Otherwise, return -1
An Example
let arr = [1,2,3];
arr.findIndex(function(value, index, array){
return value < 2;
}); // 0
let arr = [1,2,3];
arr.findIndex(function(value, index, array){
return value > 3;
}); // -1
JavaScript
How Does It Work?
Iterates through an array
Runs a callback on each value in the array
If the callback returns true for any single value, return the index at which that value is found
Otherwise, return -1
function findIndex(array, callback){
for(let i = 0; i < array.length; i++){
if(callback(array[i], i, array) === true){
return i;
}
}
return -1;
}
JavaScript
Using Findindex In A Function
function findPositionOfBoolean(list){
return list.findIndex(function(value, index, array){
return typeof value === "boolean"
});
}
findPositionOfBoolean([1,3,false,true]) // 2
findPositionOfBoolean(["no booleans", "around", "these parts"]) // -1
JavaScript
When You Would Use Findindex
You need to determine the index of a value in an array if it exists and you have to determine this by using a callback
A better version of indexOf to be used when a callback is necessary
Recap
find and findIndex iterate through an array and runs a callback on each value
if the callback at any time returns true, find returns the value or undefined if not found
if the callback at any time returns true, findIndex returns the index or -1 if not found